[Hard] Add credential documentation

[Josie123-Dev]

Task Description

Create comprehensive credential contract documentation:

• Contract overview
• Function documentation
• Parameter descriptions
• Usage examples
• Security considerations

Requirements

• Overview documentation
• Function docs
• Parameter docs
• Example code
• Security docs

Acceptance Criteria

• Overview is clear
• Functions are documented
• Parameters are described
• Examples work
• Security is covered

[rohan911438]

Would love to work on it

[grantfox-oss]

🦊 GrantFox — @rohan911438 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #98)
2. Your PR will be reviewed by the GuardZero144 maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@rohan911438's PR #114 was approved and merged by @Josie123-Dev.

🏆 @rohan911438: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (433 total points). Track your full progress on GrantFox.

👏 Great work, @rohan911438! Keep contributing to GuardZero144.